The drilling and production of oil wells require the use of various different tubular goods, such as drill pipe, casing, and tubing. The joints are provided with both a box end and a pin end, that is, a female and a male threaded surface located at the opposed marginal ends of the joint. The two threaded members constitute a threaded fastener and are designed to engage one another with friction, thereby precluding one member inadvertently being unscrewed from the other. A series of connected threaded joints are made up to form a string.
From time to time these threaded surfaces become unduly worn and must occasionally be renewed by reforming the threads at the box and pin ends. This always shortens the joint a trifle, each time the threads are renewed. Therefore, since specific lengths of a drill string are often required for specific oil well applications, it is necessary that accurate joint length calculations and recordings be made and retained.
At various stages of the drilling operations, tubular goods must be brought up from the well and elevated vertically above the drilling rig floor. This normally is accomplished with the use of a traveling block which is raised or lowered above the rig floor by means of a crown block assembly located at the top of the derrick, which is powered by a draw works or series of winches located on the rig floor, and a heavy duty wire cable system. An elevator or set of elevators is suspended beneath the traveling block by means of a drilling hook or set of bales. The traveling block assembly is lowered into proximity of the rig floor where the elevators are manually attached around the box end of the string to be raised or elevated from the hole. Normally the string is elevated in sections of three threadedly connected joints at one time called a stand of pipe. When three joints or a stand has been elevated above the rig floor, slips are inserted between the pipe and the inner surface of the rotary table up-holding the remaining portion of the string below the rig floor while the disconnection or connection is made. Each three-joint section must be measured for length as an accurate accounting of the lengths of these tubular goods is required as they are elevated from and returned to the drilling operations below the drilling rig floor.
The present art of ascertaining the length of each three-joint section consists of a steel measuring tape held from the box end to the pin end of the joint section to be measured, with the measurements being manually taken and recorded and totaled on a tally sheet. The accuracy and efficiency of this time consuming method is entirely dependent on the accuracy and efficiency of the individuals tallying and recording, which periodically allows room for inaccuracy, error, and inefficiency. Accordingly, it would be desirable to have a means by which each joint length can be measured, automatically computed, displayed, recorded, and totals displayed and recorded at will without the element of human error and inaccuracy. Such a desirable instrument is the subject of this invention.
The prior art teaches all sorts of means by which distance between two stations can be accurately measured electronically, as evidenced by the U.S. Pat. Nos. 4,136,394; 4,162,473; 4,241,430; and No. 4,281,404; respectively, issued to Jones; Utasi; Kayem, et al; and Morrow, et al; respectively, to which reference is made for the electronic details set forth therein. Reference is also made to the art cited in these four patents, and to other similar patents to be found in Class 73, 340, 364, 367, and other appropriate art areas of the U.S. Patent Office.
Jones teaches measuring between two points by the employment of a remote unit which transmits a radio pulse to a base unit. The base unit returns an acoustic or sonic signal in response to the received radio pulse. Internal logic at the remote unit determines the distance involved by using the time intervals of the signals.
Utasi teaches a transducer which generates sound waves which are directed towards a surface, and reflected to a detector, where the signal is treated to provide a measurement of the distances involved. There are numerous patents in Class 73 which illustrate various sonic and ultrasonic generators and detectors for achieving this same purpose.
Kayem, et al. determines the length of a tubular member from one end thereof by the employment of a device which produces sound pulses, and a detector which receives the pulse signal. Circuitry computes the distances involved.
Morrow, et al. discloses a sonic transducer which transmits and receives sonic impulses which are treated by circuitry in order to measure distances through water.
While others have devised various different means by which relatively short distances may be accurately measured, no one has heretofore suggested means for electronically measuring lengths of pipe supported within a derrick of a drilling rig.